Devices for transmitting torque between two rotatable shafts are known from numerous patent publications, one typical example being U.S. Pat. No. 5,469,950 from the same applicant. Here the two shafts are the output shafts of a vehicle differential mechanism. The device may accordingly in this case be called a differential brake. There may, however, be other instances when it is desired to counteract a certain rotational speed differential between two shafts, a typical example being the two shafts to the driven front and rear axle, respectively, of a four-wheel-drive vehicle.
There may be different techniques to obtain the counteracting of the rotational speed differential, but several of the known solutions rely on a hydraulic system. The device according to the patent mentioned above is one example hereof.
Hydraulic systems for the above purpose may be rather complicated and accordingly expensive to manufacture and service.
The control of different systems in a road vehicle is to a growing extent electrically performed, and different control systems often interact. The control signal to a device of the kind with which the present invention is concerned is most often electrical and is influenced by signals from other on-board systems. It would accordingly seem advantageous not to be forced to use a hydraulic system but rather an electro-mechanical system.